Up to know, airports in each local area is provided with various facilities for supporting landing of an aircraft such as a passenger aircraft. The facilities include, for example, a DVOR apparatus. The DVOR apparatus supplies directional information to the aircraft via radio waves.
Meanwhile, to operate the DVOR apparatus, a stable operation is required. Therefore, in conventional, a monitoring apparatus has been used which receives a carrier and a subcarrier from the DVOR apparatus, analyzes phases of the carrier and the subcarrier then confirms the operation of the DVOR apparatus.
Now, in a case where a monitor antenna is disposed at a short distance of 60 m or shorter away from a DVOR signal transmission antenna, since the method using the monitoring apparatus brakes phase relationships between the carrier and the subcarrier, loses amplitude information of the subcarrier and cannot perform accurate monitor processing, the monitor antenna should be disposed at a location away from 60 m or longer away from the DVOR signal transmission antenna.
Thereby, in conventional, a method, which can dispose the monitor antenna at a short distance of 60 m or shorter away from the DVOR signal transmission antenna by elimination unnecessary amplitude fluctuation of a side-band signal to be generated in receiving the side-band signal at a position of a described distance by replacing the carrier with a new carrier including a phase delay equivalent to a phase delay of the side band signal, has been proposed (e.g., Jpn. Pat. Appln. KOKAI Publication No. 4-35715).
However, the method has to pre-store wave form data of the carrier including the phase delay, then, a memory capacity is consumed by the storage of the wave form data.